mechanism of metallic cation sequestration involves the formation of complexes
between a metal ion and functional groups on the surface or inside the porous
structure of the biological material. The carboxyl groups of alginate play a major
role in the complexation. Different species of algae and the algae of the same species
may have different adsorption capacities.
Algae have many features which make them suitable candidates for removal and
concentration of selective heavy metals. They have high tolerance toward heavy
metals, ability to grow both autotrophically and heterotrophically, large surface area/
volume ratios, phototaxy, phytochelatin expression, and great potential for genetic
manipulation (Cai et al. 1995). Therefore, there is urgent need to improve algae
using genetic engineering to develop transgenic species with high accumulation
potential for heavy metals like cadmium by overexpressing phytochelatins and
metallothioneins which form complexes with cadmium and translocate them into
vacuoles to increase phytoaccumulation. Algae offer a cost- effective, less invasive,
and potentially more effective means of addressing existing heavy metal contamination than those currently practiced.
5.1.4 Phytoremediation
Phytoremediation is an environmentally friendly and cost-effective green technology which utilizes hyperaccumulator plants to extract heavy metals from soil. It is a
suitable practice to remove both organic and inorganic pollutants present in soil,
water, and the air (Gratão et al. 2005). Various mechanisms used to remediate soils
contaminated with cadmium are phytoextraction, phytostabilization, and
rhizofiltration.
5.1.4.1 Phytoextraction
The use of plants for extraction of heavy metals from contaminated soils is known as
phytoextraction. Phytoextraction efficiency depends on the chemical property of the
element removed, its uptake, translocation and accumulation by plants. It is one of
the phytoremediation strategies based on the use of green plants to remove cadmium
from soil (Salt et al. 1995). Strczynski (2000) recommended hemp and flax for
cadmium phytoextraction. Sunflower (Helianthus annuus L.) shows high tolerance
to heavy metals and is used in phytoremediation studies (Schmidt 2003; Tang et al.
2003; Pilon-Smits 2005). It can be used for cadmium removal from the high polluted
environment. Cd removal efficiency of sunflower could be 57–72%. After
phytoremediation sunflower plant must be not used in food and feed. Hadi et al.
(2015) used Ricinus communis to treat cadmium contaminants in hydroponic condition. Cd content in plant tissue was found to be increased as the dose of Cd
increased. The maximum uptake was found in root followed by leaf and then stem.
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between a metal ion and functional groups on the surface or inside the porous
structure of the biological material. The carboxyl groups of alginate play a major
role in the complexation. Different species of algae and the algae of the same species
may have different adsorption capacities.
Algae have many features which make them suitable candidates for removal and
concentration of selective heavy metals. They have high tolerance toward heavy
metals, ability to grow both autotrophically and heterotrophically, large surface area/
volume ratios, phototaxy, phytochelatin expression, and great potential for genetic
manipulation (Cai et al. 1995). Therefore, there is urgent need to improve algae
using genetic engineering to develop transgenic species with high accumulation
potential for heavy metals like cadmium by overexpressing phytochelatins and
metallothioneins which form complexes with cadmium and translocate them into
vacuoles to increase phytoaccumulation. Algae offer a cost- effective, less invasive,
and potentially more effective means of addressing existing heavy metal contamination than those currently practiced.
5.1.4 Phytoremediation
Phytoremediation is an environmentally friendly and cost-effective green technology which utilizes hyperaccumulator plants to extract heavy metals from soil. It is a
suitable practice to remove both organic and inorganic pollutants present in soil,
water, and the air (Gratão et al. 2005). Various mechanisms used to remediate soils
contaminated with cadmium are phytoextraction, phytostabilization, and
rhizofiltration.
5.1.4.1 Phytoextraction
The use of plants for extraction of heavy metals from contaminated soils is known as
phytoextraction. Phytoextraction efficiency depends on the chemical property of the
element removed, its uptake, translocation and accumulation by plants. It is one of
the phytoremediation strategies based on the use of green plants to remove cadmium
from soil (Salt et al. 1995). Strczynski (2000) recommended hemp and flax for
cadmium phytoextraction. Sunflower (Helianthus annuus L.) shows high tolerance
to heavy metals and is used in phytoremediation studies (Schmidt 2003; Tang et al.
2003; Pilon-Smits 2005). It can be used for cadmium removal from the high polluted
environment. Cd removal efficiency of sunflower could be 57–72%. After
phytoremediation sunflower plant must be not used in food and feed. Hadi et al.
(2015) used Ricinus communis to treat cadmium contaminants in hydroponic condition. Cd content in plant tissue was found to be increased as the dose of Cd
increased. The maximum uptake was found in root followed by leaf and then stem.
374
S. Saini and G. Dhania